This application proposes to study the mechanism of muscarinic and peptidergic receptor mediated changes in electrical properties, intracellular calcium concentration, and secretion of catecholamines (CA). For this purpose chromaffin cells of adrenals derived from 4- to 5-week-old rats will be cultured. Patch clamp techniques will be used to measure changes in membrane potential and calcium current, Indo-1 fluorescence and laser photometry to quantitate intracellular calcium and electrochemical detection to monitor exocytotic secretion of CA. Laser photometry and electrochemistry will be combined to simultaneously monitor changes in intracellular calcium and exocytosis from the same cell on an identical, subsecond time scale.